Date of Award

27-1-2024

Document Type

Thesis

School

School of Mechanical Engineering

Programme

Ph.D.-Doctoral of Philosophy

First Advisor

S.Nadaraja Pillai

Keywords

Wind Tunnel Testing, Airfoil Trailing Edge Modification, Engineering and Technology, Engineering, Engineering Aerospace

Abstract

Lift (upward force) is a significant aerodynamic component that directly relates to the aerodynamic efficiency (lift-to-drag ratio) of the airfoil. Enhancement of airfoil lift is important for industries like wind turbines, aircraft, and turbo machinery. The present study investigates the NACA series airfoil by modifying the trailing edge in the form of extension and serration. The angle of attack was changed from 0° to 35° instep of 5°, and the airflow Reynolds number was fixed as 2.14 × 105. To figure out the flow behavior, surface pressure has been collected from the 50 pressure ports provided over the airfoil surface. The extended trailing edge of amplitude (10%c, 20%c, and 30%c) is designed and fitted with the conventional airfoil.

Further, the triangular serration is introduced with the wavelengths of 20%c, 40%c, and 60%c and equipped with the conventional airfoil at the trailing edge and tested in the wind tunnel. The change in surface pressure coefficient and aerodynamic force coefficient are presented. As a result, excellent lift increment is favoured by the extended trailing edge, a thin, long surface attached to a conventional airfoil. By modifying the flow pattern, the serrated trailing edge functions as a flow control mechanism, delaying the stall phenomenon.

Airfoils employed in aircraft wings or turbine blades exposes to open atmosphere, where the turbulence intensity (measure of air stability) often changes. Turbulence intensity is measured by calculating the ratio of fluctuated velocity (u’) to the mean velocity (u∞) for a particular sampling frequency, in the current work the sampling frequency was fixed as 850 Hz.

The conventional airfoil, with and without extended and serrated trailing edges, of all designed cases is tested under the turbulence intensity (T. I) of 0.3%, 3%, 5%, 7% and 12%. On reaching T. I values of 7% and beyond, the lift performance falls, as at higher freestream turbulence, the complication takes place between the interaction of freestream turbulence and flow adjacent to the airfoil surface. This makes the aerodynamic performance to fall at very higher turbulence intensity.

However, the lift value falls very smoothly (i.e. soft stall), as alpha is increased. This is the similar trend of trailing edge stall, the separation point moves downstream nearer to the trailing edge at higher freestream turbulence intensity. However due to increase in friction drag, the aerodynamic efficiency falls with conserved stall characteristics. The airfoil with extended trailing edge and serrated trailing edge performs well compared to the conventional airfoil, even at higher levels of turbulence intensity.

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